"Survey return zero cross section" for a pp EPA process when going above sqrt(s)~31 TeV

Asked by David d'Enterria (CERN) on 2019-04-15

Hi,

I'm running this simple process: gamma gamma-> b bbar in pp collisions (EPA photon flux) as a function of sqrt(s) with MG5_aMC_v2_6_5. The following piece of code works fine for all c.m. up to sqrt(s)~31 TeV:

import model sm
generate a a > b b~ QED=99
output tmp
launch
0
set mH 125.
set mmbb 100. ! min invariant mass of a b pair
set mmbbmax 150. ! max invariant mass of a b pair
set lpp 2
set ebeam1 15500
set ebeam2 15000
0

When setting the ebeam1, ebeam2 energies above ~16 TeV each, the code invariably throws an error:

Survey return zero cross section.
   Typical reasons are the following:
   1) A massive s-channel particle has a width set to zero.
   2) The pdf are zero for at least one of the initial state particles
      or you are using maxjetflavor=4 for initial state b:s.
   3) The cuts are too strong.
   Please check/correct your param_card and/or your run_card.

What's the reason for such a behaviour? How can I cure it ?

Thanks. Below the run and parameter cards:

-------------------------------------------------------------------------------------------------------------------------------------

cat tmp/Cards/run_card.dat
#*********************************************************************
# MadGraph5_aMC@NLO *
# *
# run_card.dat MadEvent *
# *
# This file is used to set the parameters of the run. *
# *
# Some notation/conventions: *
# *
# Lines starting with a '# ' are info or comments *
# *
# mind the format: value = variable ! comment *
# *
# To display more options, you can type the command: *
# update full_run_card *
#*********************************************************************
#
#*******************
# Running parameters
#*******************
#
#*********************************************************************
# Tag name for the run (one word) *
#*********************************************************************
  tag_1 = run_tag ! name of the run
#*********************************************************************
# Number of events and rnd seed *
# Warning: Do not generate more than 1M events in a single run *
# If you want to run Pythia, avoid more than 50k events in a run. *
#*********************************************************************
  10000 = nevents ! Number of unweighted events requested
  0 = iseed ! rnd seed (0=assigned automatically=default))
#*********************************************************************
# Collider type and energy *
# lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
# 3=photon from electron *
#*********************************************************************
  2 = lpp1 ! beam 1 type
  2 = lpp2 ! beam 2 type
  15500.0 = ebeam1 ! beam 1 total energy in GeV
  15500.0 = ebeam2 ! beam 2 total energy in GeV
# To see polarised beam options: type "update beam_pol"
#*********************************************************************
# PDF CHOICE: this automatically fixes also alpha_s and its evol. *
#*********************************************************************
  nn23lo1 = pdlabel ! PDF set
  230000 = lhaid ! if pdlabel=lhapdf, this is the lhapdf number
# To see heavy ion options: type "update ion_pdf"
#*********************************************************************
# Renormalization and factorization scales *
#*********************************************************************
  False = fixed_ren_scale ! if .true. use fixed ren scale
  False = fixed_fac_scale ! if .true. use fixed fac scale
  91.188 = scale ! fixed ren scale
  91.188 = dsqrt_q2fact1 ! fixed fact scale for pdf1
  91.188 = dsqrt_q2fact2 ! fixed fact scale for pdf2
  -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
  1.0 = scalefact ! scale factor for event-by-event scales
#*********************************************************************
# Type and output format
#*********************************************************************
  False = gridpack !True = setting up the grid pack
  -1.0 = time_of_flight ! threshold (in mm) below which the invariant livetime is not written (-1 means not written)
  3.0 = lhe_version ! Change the way clustering information pass to shower.
  True = clusinfo ! include clustering tag in output
  average = event_norm ! average/sum. Normalization of the weight in the LHEF

#*********************************************************************
# Matching parameter (MLM only)
#*********************************************************************
  0 = ickkw ! 0 no matching, 1 MLM
  1.0 = alpsfact ! scale factor for QCD emission vx
  False = chcluster ! cluster only according to channel diag
  4 = asrwgtflavor ! highest quark flavor for a_s reweight
  False = auto_ptj_mjj ! Automatic setting of ptj and mjj if xqcut >0
                                   ! (turn off for VBF and single top processes)
  0.0 = xqcut ! minimum kt jet measure between partons
#*********************************************************************
#
#*********************************************************************
# handling of the helicities:
# 0: sum over all helicities
# 1: importance sampling over helicities
#*********************************************************************
  0 = nhel ! using helicities importance sampling or not.
#*********************************************************************
# Generation bias, check the wiki page below for more information: *
# 'cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LOEventGenerationBias' *
#*********************************************************************
  None = bias_module ! Bias type of bias, [None, ptj_bias, -custom_folder-]
  {} = bias_parameters ! Specifies the parameters of the module.
#
#*******************************
# Parton level cuts definition *
#*******************************
#
#
#*********************************************************************
# BW cutoff (M+/-bwcutoff*Gamma) ! Define on/off-shell for "$" and decay
#*********************************************************************
  15.0 = bwcutoff ! (M+/-bwcutoff*Gamma)
#*********************************************************************
# Apply pt/E/eta/dr/mij/kt_durham cuts on decay products or not
# (note that etmiss/ptll/ptheavy/ht/sorted cuts always apply)
#*********************************************************************
  False = cut_decays ! Cut decay products
#*********************************************************************
# Standard Cuts *
#*********************************************************************
# Minimum and maximum pt's (for max, -1 means no cut) *
#*********************************************************************
  20.0 = ptj ! minimum pt for the jets
  0.0 = ptb ! minimum pt for the b
  10.0 = pta ! minimum pt for the photons
  10.0 = ptl ! minimum pt for the charged leptons
  0.0 = misset ! minimum missing Et (sum of neutrino's momenta)
  -1.0 = ptjmax ! maximum pt for the jets
  -1.0 = ptbmax ! maximum pt for the b
  -1.0 = ptamax ! maximum pt for the photons
  -1.0 = ptlmax ! maximum pt for the charged leptons
  -1.0 = missetmax ! maximum missing Et (sum of neutrino's momenta)
  {} = pt_min_pdg ! pt cut for other particles (use pdg code). Applied on particle and anti-particle
  {} = pt_max_pdg ! pt cut for other particles (syntax e.g. {6: 100, 25: 50})
#*********************************************************************
# Minimum and maximum E's (in the center of mass frame) *
#*********************************************************************
  0.0 = ej ! minimum E for the jets
  0.0 = eb ! minimum E for the b
  0.0 = ea ! minimum E for the photons
  0.0 = el ! minimum E for the charged leptons
  -1.0 = ejmax ! maximum E for the jets
  -1.0 = ebmax ! maximum E for the b
  -1.0 = eamax ! maximum E for the photons
  -1.0 = elmax ! maximum E for the charged leptons
  {} = e_min_pdg ! E cut for other particles (use pdg code). Applied on particle and anti-particle
  {} = e_max_pdg ! E cut for other particles (syntax e.g. {6: 100, 25: 50})
#*********************************************************************
# Maximum and minimum absolute rapidity (for max, -1 means no cut) *
#*********************************************************************
  5.0 = etaj ! max rap for the jets
  -1.0 = etab ! max rap for the b
  2.5 = etaa ! max rap for the photons
  2.5 = etal ! max rap for the charged leptons
  0.0 = etajmin ! min rap for the jets
  0.0 = etabmin ! min rap for the b
  0.0 = etaamin ! min rap for the photons
  0.0 = etalmin ! main rap for the charged leptons
  {} = eta_min_pdg ! rap cut for other particles (use pdg code). Applied on particle and anti-particle
  {} = eta_max_pdg ! rap cut for other particles (syntax e.g. {6: 2.5, 23: 5})
#*********************************************************************
# Minimum and maximum DeltaR distance *
#*********************************************************************
  0.4 = drjj ! min distance between jets
  0.0 = drbb ! min distance between b's
  0.4 = drll ! min distance between leptons
  0.4 = draa ! min distance between gammas
  0.0 = drbj ! min distance between b and jet
  0.4 = draj ! min distance between gamma and jet
  0.4 = drjl ! min distance between jet and lepton
  0.0 = drab ! min distance between gamma and b
  0.0 = drbl ! min distance between b and lepton
  0.4 = dral ! min distance between gamma and lepton
  -1.0 = drjjmax ! max distance between jets
  -1.0 = drbbmax ! max distance between b's
  -1.0 = drllmax ! max distance between leptons
  -1.0 = draamax ! max distance between gammas
  -1.0 = drbjmax ! max distance between b and jet
  -1.0 = drajmax ! max distance between gamma and jet
  -1.0 = drjlmax ! max distance between jet and lepton
  -1.0 = drabmax ! max distance between gamma and b
  -1.0 = drblmax ! max distance between b and lepton
  -1.0 = dralmax ! maxdistance between gamma and lepton
#*********************************************************************
# Minimum and maximum invariant mass for pairs *
# WARNING: for four lepton final state mmll cut require to have *
# different lepton masses for each flavor! *
#*********************************************************************
  0.0 = mmjj ! min invariant mass of a jet pair
  100.0 = mmbb ! min invariant mass of a b pair
  0.0 = mmaa ! min invariant mass of gamma gamma pair
  0.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
  -1.0 = mmjjmax ! max invariant mass of a jet pair
  150.0 = mmbbmax ! max invariant mass of a b pair
  -1.0 = mmaamax ! max invariant mass of gamma gamma pair
  -1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
  {} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
  {'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
                       ! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
#*********************************************************************
# Minimum and maximum invariant mass for all letpons *
#*********************************************************************
  0.0 = mmnl ! min invariant mass for all letpons (l+- and vl)
  -1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
#*********************************************************************
# Minimum and maximum pt for 4-momenta sum of leptons *
#*********************************************************************
  0.0 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)
  -1.0 = ptllmax ! Maximum pt for 4-momenta sum of leptons(l and vl)
#*********************************************************************
# Inclusive cuts *
#*********************************************************************
  0.0 = ptheavy ! minimum pt for at least one heavy final state
  0.0 = xptj ! minimum pt for at least one jet
  0.0 = xptb ! minimum pt for at least one b
  0.0 = xpta ! minimum pt for at least one photon
  0.0 = xptl ! minimum pt for at least one charged lepton
#*********************************************************************
# Control the pt's of the jets sorted by pt *
#*********************************************************************
  0.0 = ptj1min ! minimum pt for the leading jet in pt
  0.0 = ptj2min ! minimum pt for the second jet in pt
  0.0 = ptj3min ! minimum pt for the third jet in pt
  0.0 = ptj4min ! minimum pt for the fourth jet in pt
  -1.0 = ptj1max ! maximum pt for the leading jet in pt
  -1.0 = ptj2max ! maximum pt for the second jet in pt
  -1.0 = ptj3max ! maximum pt for the third jet in pt
  -1.0 = ptj4max ! maximum pt for the fourth jet in pt
  0 = cutuse ! reject event if fails any (0) / all (1) jet pt cuts
#*********************************************************************
# Control the pt's of leptons sorted by pt *
#*********************************************************************
  0.0 = ptl1min ! minimum pt for the leading lepton in pt
  0.0 = ptl2min ! minimum pt for the second lepton in pt
  0.0 = ptl3min ! minimum pt for the third lepton in pt
  0.0 = ptl4min ! minimum pt for the fourth lepton in pt
  -1.0 = ptl1max ! maximum pt for the leading lepton in pt
  -1.0 = ptl2max ! maximum pt for the second lepton in pt
  -1.0 = ptl3max ! maximum pt for the third lepton in pt
  -1.0 = ptl4max ! maximum pt for the fourth lepton in pt
#*********************************************************************
# Control the Ht(k)=Sum of k leading jets *
#*********************************************************************
  0.0 = htjmin ! minimum jet HT=Sum(jet pt)
  -1.0 = htjmax ! maximum jet HT=Sum(jet pt)
  0.0 = ihtmin !inclusive Ht for all partons (including b)
  -1.0 = ihtmax !inclusive Ht for all partons (including b)
  0.0 = ht2min ! minimum Ht for the two leading jets
  0.0 = ht3min ! minimum Ht for the three leading jets
  0.0 = ht4min ! minimum Ht for the four leading jets
  -1.0 = ht2max ! maximum Ht for the two leading jets
  -1.0 = ht3max ! maximum Ht for the three leading jets
  -1.0 = ht4max ! maximum Ht for the four leading jets
#***********************************************************************
# Photon-isolation cuts, according to hep-ph/9801442 *
# When ptgmin=0, all the other parameters are ignored *
# When ptgmin>0, pta and draj are not going to be used *
#***********************************************************************
  0.0 = ptgmin ! Min photon transverse momentum
  0.4 = r0gamma ! Radius of isolation code
  1.0 = xn ! n parameter of eq.(3.4) in hep-ph/9801442
  1.0 = epsgamma ! epsilon_gamma parameter of eq.(3.4) in hep-ph/9801442
  True = isoem ! isolate photons from EM energy (photons and leptons)
#*********************************************************************
# WBF cuts *
#*********************************************************************
  0.0 = xetamin ! minimum rapidity for two jets in the WBF case
  0.0 = deltaeta ! minimum rapidity for two jets in the WBF case
#***********************************************************************
# Turn on either the ktdurham or ptlund cut to activate *
# CKKW(L) merging with Pythia8 [arXiv:1410.3012, arXiv:1109.4829] *
#***********************************************************************
  -1.0 = ktdurham
  0.4 = dparameter
  -1.0 = ptlund
  1, 2, 3, 4, 5, 6, 21 = pdgs_for_merging_cut ! PDGs for two cuts above
#*********************************************************************
# maximal pdg code for quark to be considered as a light jet *
# (otherwise b cuts are applied) *
#*********************************************************************
  4 = maxjetflavor ! Maximum jet pdg code
#*********************************************************************
#
#*********************************************************************
# Store info for systematics studies *
# WARNING: Do not use for interference type of computation *
#*********************************************************************
  True = use_syst ! Enable systematics studies
#
  systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments ! see: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Systematics#Systematicspythonmodule
# Syscalc is deprecated but to see the associate options type'update syscalc'#*********************************************************************
# Additional hidden parameters
#*********************************************************************
  ['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments # Choose the argment to pass to the systematics command. like --mur=0.25,1,4. Look at the help of the systematics function for more details.

-------------------------------------------------------------------------------------------------------------------------------------
 cat tmp/Cards/param_card.dat
######################################################################
## PARAM_CARD AUTOMATICALY GENERATED BY MG5 ####
######################################################################
###################################
## INFORMATION FOR MASS
###################################
BLOCK MASS #
      5 4.700000e+00 # mb
      6 1.730000e+02 # mt
      15 1.777000e+00 # mta
      23 9.118800e+01 # mz
      25 1.250000e+02 # mh
      1 0.000000e+00 # d : 0.0
      2 0.000000e+00 # u : 0.0
      3 0.000000e+00 # s : 0.0
      4 0.000000e+00 # c : 0.0
      11 0.000000e+00 # e- : 0.0
      12 0.000000e+00 # ve : 0.0
      13 0.000000e+00 # mu- : 0.0
      14 0.000000e+00 # vm : 0.0
      16 0.000000e+00 # vt : 0.0
      21 0.000000e+00 # g : 0.0
      22 0.000000e+00 # a : 0.0
      24 8.041900e+01 # w+ : cmath.sqrt(mz__exp__2/2. + cmath.sqrt(mz__exp__4/4. - (aew*cmath.pi*mz__exp__2)/(gf*sqrt__2)))
###################################
## INFORMATION FOR SMINPUTS
###################################
BLOCK SMINPUTS #
      1 1.325070e+02 # aewm1
      2 1.166390e-05 # gf
      3 1.180000e-01 # as
###################################
## INFORMATION FOR YUKAWA
###################################
BLOCK YUKAWA #
      5 4.700000e+00 # ymb
      6 1.730000e+02 # ymt
      15 1.777000e+00 # ymtau
###################################
## INFORMATION FOR DECAY
###################################
DECAY 6 1.491500e+00 # wt
DECAY 23 2.441404e+00 # wz
DECAY 24 2.047600e+00 # ww
DECAY 25 6.382339e-03 # wh
DECAY 1 0.000000e+00 # d : 0.0
DECAY 2 0.000000e+00 # u : 0.0
DECAY 3 0.000000e+00 # s : 0.0
DECAY 4 0.000000e+00 # c : 0.0
DECAY 5 0.000000e+00 # b : 0.0
DECAY 11 0.000000e+00 # e- : 0.0
DECAY 12 0.000000e+00 # ve : 0.0
DECAY 13 0.000000e+00 # mu- : 0.0
DECAY 14 0.000000e+00 # vm : 0.0
DECAY 15 0.000000e+00 # ta- : 0.0
DECAY 16 0.000000e+00 # vt : 0.0
DECAY 21 0.000000e+00 # g : 0.0
DECAY 22 0.000000e+00 # a : 0.0

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
David d'Enterria (CERN)
Solved:
2019-04-15
Last query:
2019-04-15
Last reply:
2019-04-15

It's a phase-space integration error. Related to the fact that your cut are quite strong.

Fixing this require a lot of expertise. The easiest is likely that you build your own phase-space integrator tune for your cut.

If you had a s-channel resonances inside your Feynman diagram.
then you could have edit genps.f to force smax to be 150^2
and then run only with that channel of integration. (

But you do not have such diagram in your case.

Cheers,

Olivier

David d'Enterria (CERN) (dde) said : #2

Thanks for your quick response.

I enlarged the m_inv(bbbar) window and it worked now.

cheers, david